howitzer vs high-angle gun

howitzer and high-angle gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
howitzer	Yes	No	No	No
high-angle gun	Yes	No	No	No

As nouns, high-angle gun is a hypernym of howitzer; that is, high-angle gun is a word with a broader meaning than howitzer:

howitzer: a muzzle-loading high-angle gun with a short barrel that fires shells at high elevations for a short range
high-angle gun: a cannon that can be fired at a high elevation for relatively short ranges

howitzer (noun)	high-angle gun (noun)
a muzzle-loading high-angle gun with a short barrel that fires shells at high elevations for a short range	a cannon that can be fired at a high elevation for relatively short ranges